The present invention relates to the field of polymers and the subject of the invention is compositions based on fluorinated polymer(s) and their method of preparation.
Fluorinated homopolymers and copolymers are known for their good thermal withstand capability, their chemical resistance, especially to solvents, weatherability and resistance to radiation (UV, etc.), their impermeability to gases and to liquids, and their property of being electrical insulants. They are used in particular for the production of pipes for conveying hydrocarbons extracted from off-shore or on-shore oil deposits. The hydrocarbons are sometimes transported at high temperatures (of about 135xc2x0 C.) and at a high pressure (for example 70 MPa). Severe problems therefore arise, during operation of installations, relating to the mechanical, thermal and chemical resistance of the materials employed. Other requirements are added to them before or after service: thus, during their production, their installation and/or their removal (reeling/unreeling), the pipes may be subjected to impacts and to flexural loads which they must also withstand and, sometimes, they must do so at particularly low temperatures (for example xe2x88x9235xc2x0 C.).
In order to try to meet these short-term and long-term requirements, various types of materials have been proposed, generally comprising one or more metallic components which guarantee mechanical rigidity, for example a spiralled steel tape, as well as various layers based on polymeric compositions, which in particular provide impermeability and thermal insulation. These compositions, often based on semicrystalline fluorinated polymers, especially poly(vinylidene fluoride) (PVDF), are often plasticized in order to remedy a lack of flexibility, a low elongation at the yield point and an insufficient toughness, this having the drawback of the plasticizers being extracted relatively rapidly by the hydrocarbons transported, gradually resulting in a loss of the properties provided by the plasticization (flexibility, toughness, etc.), being accompanied in general by shrinkage phenomena and consequently limiting the lifetime of the articles based on these compositions.
In order to solve some of these problems, the optionally plasticized fluorinated polymers have been replaced by polymeric compositions comprising a PVDF homopolymer, a thermoplastic copolymer of vinylidene fluoride (VF2) and of at least one other fluorinated monomer (EP 608,939 and EP 608,940) and a plasticizer (EP 608,939). However, strict and precise control of the morphology of such blends demands the use of complex and expensive apparatus which therefore makes this technical solution not easily realisable; moreover, it is found that these blends have a limited toughness at low temperature and a poor swelling resistance, for example when in contact with hydrocarbons, and a chemical withstand capability which is inferior to that of PVDF by itself, and any plasticizer is extracted when in contact with certain chemicals.
Elastomeric particles have also been incorporated into PVDF (FR 2,592,655 and FR 2,618,791) for the purpose of absorbing the hydrocarbons and of fixing them throughout the blend, the proportion of elastomer within the blend having not to exceed 25% of the total mass. Such blends have improved toughness over PVDF alone, but their flexibility is insufficient for certain applications envisaged, especially for the transportation and/or storage of hydrocarbons, as this type of blend is not very flexible when not in direct contact with the hydrocarbons. FR 2,592,655 has described blends containing, in addition, at least 10% by weight of plasticizer, which, although they possess both the desired flexibility and the desired impact strength, sooner or later let the plasticizer exude.
Patent Application EP 0,714,944 describes compositions comprising a PVDF matrix in which are dispersed nodules of vulcanized elastomers which are optionally flexibilized by plasticizers. The multiaxial impact strength of these compositions is very good, but the amount of elastomer, 26.6 or 50 parts by weight per 100 parts by weight of PVDF 1000 (Examples 6 and 11), is so high that these compositions lack thermal and chemical stability at 150xc2x0 C. In addition, these compositions have the drawback of a high permeability under pressure and a poor resistance to the rapid decompression of hot pressurized gases (xe2x80x9cblisteringxe2x80x9d).
The present invention aims to solve the abovementioned technical problems and the subject of the invention is a flexible and tough composition comprising:
at least one homopolymer (A) of vinylidene fluoride (VF2) or a copolymer (A) of VF2 and of at least one other monomer copolymerizable with VF2, in which the said monomer is present in an amount of between 0 and 30 parts by weight per 100 parts by weight of VF2,
at least one elastomer B,
at least one plasticizer C,
characterized in that, on the one hand, the said composition comprises from 0.5 to 10 parts by weight of B and from 0.5 to 10 parts by weight of C per 100 parts by weight of A, with the additional condition that the sum of B and C is from 1 to 10.5 parts by weight and, on the other hand, in that the homopolymer or the copolymer of vinylidene fluoride, A, is chosen in such a way that it has a melt flow index, measured according to the ISO 1133 standard at 230xc2x0 C. under a load of 5 kg, of less than 5 g/10 min and a critical modulus GC, at the intersection of the melt shear moduli Gxe2x80x2 and Gxe2x80x3 measured at 190xc2x0 C., of between 5 and 22 kPa, the said composition having the following properties:
an elongation at the yield point, xcex5y, of greater than 11%, an elongation at break xcex5b of greater than 200%, an impact strength at 23xc2x0 C. of greater than 50 kJ/m2 and an impact strength at xe2x88x9230xc2x0 C. of greater than 10 kJ/m2, these being measured according to the ISO 180-1982 standard, a resistance to flexural rupture on a sleeved metal tape of greater than 50%, a weight loss xcex94w in air at 150xc2x0 C. for 1 month of less than or equal to 8% and a weight change xcex94p in petroleum (equal-volume mixture of cyclohexane, isooctane and xylene) at 150xc2x0 C. for 1 month which is not negative (the said composition does not lose weight in petroleum).
The critical modulus GC is determined at 190xc2x0 C. using a dynamic mechanical spectrometer, for example of the Rheometrics RMS 800 type, using a 25 mm diameter planexe2x80x94plane viscometer.
Preferably, the said other monomer is present in a relative amount of between 0 and 5 parts by weight.
Preferably, the said other monomer is a fluorinated monomer.
Advantageously, B is present in a relative amount of from 0.5 to 5 parts by weight per 100 parts by weight of A.
Advantageously, C is present in a relative amount of from 0.5 to 5 parts by weight per 100 parts by weight of A.
The fluorinated polymers A of the compositions according to the invention are chosen from homopolymers or copolymers of VF2 because of their excellent chemical inertness in the presence of crude gas or petroleum and because of their high-temperature stability.
Preferably, the compositions according to the invention comprise 100 parts by weight of vinylidene fluoride homopolymer, 2.1 parts by weight of B and 3.2 parts by weight of C, the homopolymer being chosen so as to have an MFI measured at 230xc2x0 C., of 0.7 and a critical modulus GC, measured at 190xc2x0 C., of 20 kPa.
Advantageously; with regard to the latter compositions, B is an acrylic elastomer and C is dibutyl sebacate.
The elastomers B which can be used in the context of the invention may be chosen from true elastomers and thermoplastic elastomers (TPEs). True elastomers or rubbers, whether natural or synthetic, are defined by the ASTM, Special Technical Bulletin No. 184 standard as materials capable of being drawn, at room temperature, up to twice their natural length and which, once released after being held under tension for 5 minutes, recover, to within 10, their initial length in the same time. TPEs have an elongation at the yield point of greater than 15%. TPEs lie between thermoplastic resins, with easy and varied processing but with limited temperature properties or limited properties in the dynamic domain, and elastomers with remarkable elastic properties, but whose processing is expensive, complex and often polluting. The structure of TPEs is always composed of two incompatible phases, one of them resembling the thermoplastic blocks dispersed in the elastomer phase. In general, 5 categories of TPE may be distinguished:
thermoplastic polyolefin (TPO) elastomers are physical blends based on polyolefins. A distinction may be made between those which contain more than 60% of polypropylene and those whose elastomer phase is predominant (greater than 70%), it being possible for the latter to be crosslinked or uncrosslinked,
polystyrene-based block copolymers, the hard phase of which consists of polystyrene blocks, it being possible for the soft phase to be formed, for example, by polybutadiene blocks (SBS), polyisoprene blocks (SIS) or poly(ethylene-butylene) blocks (SEBS),
block copolymers based on polyurethane (TPUs) which may be obtained by the conjoint reaction of a diol of high molecular mass, which constitutes the soft crystallizable block of the TPE, with a diisocyanate and a diol of low molecular mass which generate the hard block,
polyester-based block copolymers such as those obtained by the copolymerization of a polybutylene (PBT) or of a polyethylene terephthalate (PET) which constitutes the hard crystalline blocks and of a glycol of low molecular weight (butanediol, diethylene glycol) which, combined with a polyalkylene ether glycol, forms the crystallizable soft block,
polyamide-based block copolymers such as those in which the hard blocks consist of polyamide (PA) and the crystallizable soft blocks of polyether, these also being called polyetheramides, as well as polyesteramides.
The elastomers and TPEs may advantageously be chosen from natural rubbers, polyurethanes, ethylene-propylene-maleicized diene copolymers (EPDM), acrylonitrile-butadiene-styrene copolymers (ABS), methyl methacrylate-butadiene-styrene copolymers (MBS), polyamide-based block copolymers (polyetheramides, polyesteramides, polyetheresteramides), ethylene-carbon monoxide copolymers, acrylic rubbers, especially core-shell particles with a polyacrylic skin, SBS, SIS, ethylene-ethyl acrylate copolymers, ethylene-ethyl acetate copolymers, ethylene-vinyl acetate copolymers, as well as their terpolymers.
Preferably, the elastomer B is chosen from methyl methacrylate-butadiene-styrene copolymers (MBS) and acrylic rubbers.
Advantageously, the acrylic rubber is in the form of core-shell particles with a polyacrylic skin.
The plasticizers C may be chosen from the usual plasticizers and especially those described in U.S. Pat. No. 3,541,039 and U.S. Pat. No. 4,584,215. Preferably, the plasticizer is chosen from dibutyl sebacate and N-n-butylsulphonamide.
Apart from the constituents A, B and C described above, the compositions according to the invention may contain various organic or inorganic, macromolecular or non-macromolecular additives and/or fillers and/or colorants and/or pigments well known in the literature.
By way of non-limiting examples of fillers, mention may be made of mica, alumina, talc, carbon black, glass fibres, carbon fibres and macromolecular compounds.
By way of non-limiting examples of additives, mention may be made of UV stabilizers, fire retardants, heat stabilizers and processing aids.
The sum of these various additives and fillers generally represents less than 20% of the total mass A+B+C.
Advantageously, the preparation of the compositions according to the invention is carried out by melt blending the components A, B and C.
The composition according to the invention may be prepared by melt blending the vinylidene homopolymer or copolymer A with the elastomer or elastomers Bxe2x80x94initially in the form of powders or granulesxe2x80x94in an extruder, a multiple-roll mixer or any type of suitable mixing apparatus.
It is also possible to blend a latex of a vinylidene homopolymer or copolymer with the elastomer or elastomers in powder or latex form.
The plasticizer or plasticizers together with the optional additives may be incorporated into the compositions during the blending of A and B, or are blended with one or other of these constituents prior to the step of blending A and B, or after blending A and B using the mixing techniques mentioned above.
The compositions according to the invention may be used for producing materials exposed to stresses under high-temperature and/or low-temperature conditions, in contact with particularly aggressive substances (such as hydrocarbons, strong acids, solvents, inorganic and organic bases) during which their toughness and flexibility properties are particularly required.
As indicated above, the compositions according to the invention are particularly suitable for manufacturing the impermeable sleeves of flexible metal pipes for the extraction and/or transportation of gases and hydrocarbons in the oil and gas industries.
These impermeable sleeves are generally in the form of monolayer or multilayer tubes, manufactured by extrusion or coextrusion, into which the flexible metal pipe is then inserted, or else they are formed directly around the flexible pipe using the standard overjacketing techniques.
The composition according to the invention may be used in multilayer impermeable sleeves such as those described, for example, in U.S. Pat. No. 5,601,893.
The compositions according to the invention are also well suited for producing, by extrusion, chemical engineering components, especially in the form of pipes and tubes, as well as for producing objects in the civil engineering and building industries, such as cable sheaths, stays, as well as monolayer or multilayer films and sheets for any kind of industry.
The composition according to the invention may also be used in sleeves of wires, ropes, cables and stays, such as those described in Patent Applications EP 671,502 and EP 671,746.